Remove some small unused functions
Remove _api_helpers.py file, only had one tiny function
Add some minimal release notes
Remove caching of the unbound_single_ckernel creation, to simplify things for now

The caching makes the code a bit more complicated to deal with, we
can live with redundant recompilation for now while the code needs
to mutate a lot.
Move some llvm-related code from blaze_kernels.py to llutil.py
Remove shapefunc as a parameter to the BlazeElementKernel constructor

because it's not being used/tested by anything. It can be added back
when a use case calls for it.
Move the ckernel jit compiling from a blaze kernel to a separate file